The prime minister's refusal to engage with moderate MPs has led her into the impasse that now makes it so hard to strike a deal in Brussels

Theresa May's failure to make progress in Brexit talks this week is a function of having to conduct parallel negotiations, one at home and one abroad. The two conversations overlap, but rhetoric that animates the domestic debate can be far removed from the arguments the prime minister encounters across the Channel.

This is most evident in discussion of arrangements for Northern Ireland – the main obstacle to a withdrawal agreement. In Brussels, the issues are seen in terms of legal commitments: enforcement of the EU's single market rules across post-Brexit borders; the Good Friday agreement, which makes the border question uniquely sensitive; and the December 2017 deal that sealed the first phase of exit talks. In that document the UK signed up to the “backstop”, keeping Northern Ireland aligned with EU regulations (thereby obviating the need for a restored border with the Irish Republic) in the event that no more innovative solution could be found.